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Investigation of potential roles of Phospholipase D in Arabidopsis thaliana seed oil accumulation Yu, Yuanyuan

Abstract

Most plants depend on the production of storage compounds in the seed to provide nutrients during germination. These storage compounds have been exploited by man for a variety of purposes. For example vegetable oil is an important lipid source for cooking and the production of lubricants, inks, paints, and biodiesels. Almost all seed oil is stored in the chemical form of triacylglycerol (TAG), and in mature seed, TAG is stored in densely packed oil bodies. Genetic engineering offers great potential to increase the amount and/or manipulate the type of oil produced. There are two routes to this goal: first, the development of existing plant species that already synthesize the desired novel oil into “alternative oilseed’ crops; second, the engineering of existing crops through the cloning of genes which determine the synthesis of novel oils and their introduction into existing crops such as oilseed rape (Brassica napus) by genetic transformation. Whichever approach is adopted we need to know how storage oil is accumulated in order to optimize yield. My research is part of a broader effort to explore the possibility of increasing oil content in Brassica species using Arabidopsis thaliana as a model system. My specific project examines whether the phospholipase D zeta (PLDZ) enzyme can be used to control oil production in Arabidopsis thaliana. In plants, PLDZ hydrolyzes membrane phospholipids to form phosphatidic acid, which is the branch point for the synthesis of diacyiglycerol that is an immediate precursor of storage oil. In addition, previous research had shown that the PLDZ gene was negatively regulated in the leaves by GLABRA 2 (GL2), a transcription factor that was also known to negatively regulate oil content in the seed. In this thesis I show that the pldzlpldz2 double mutant accumulates 11% less oil in the seed than did wild type, without differences in seed size, plant growth or development. Both PLDZ genes localize to the embryo and funiculus during the later stages of seed development. In the g12 mutant background, PLDZ transcript levels in the seeds are lower than in the wild type; besides the pldz]pldz2gl2 triple mutant shows intermediate oil content which is unlike neither pldzlpldz2 double mutant nor g12 mutant phenotype, suggesting that GL2 is not a negative regulator of PLDZ genes during oil production process.

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